trigonometry - Finding the amplitude of a trigonometric function

I have the following function:

$$f(x)=\sqrt{3}\cos (x)+\sin(x)$$

I am trying to find what the amplitude of this function is without graphing it. I understand the formula for a cosine equation is:

$$y=A\cos(Bx-C)$$

Where A is the amplitude, meaning that $\sqrt{3}$ would be the amplitude, but that answer is incorrect. How do you get the amplitude without having to graph?